I read this short story some time ago, and happened upon it again late last week while browsing the Internet. It's a personal favorite, since it is so expansive while still being realtively short. Asimov's own words describe it best:

Quote from: Isaac Asimov

This is by far my favorite story of all those I have written.

After all, I undertook to tell several trillion years of human history in the space of a short story and I leave it to you as to how well I succeeded. I also undertook another task, but I won't tell you what that was lest l spoil the story for you.

It is a curious fact that innumerable readers have asked me if I wrote this story. They seem never to remember the title of the story or (for sure) the author, except for the vague thought it might be me. But, of course, they never forget the story itself especially the ending. The idea seems to drown out everything -- and I'm satisfied that it should.

Necroing is when you bring up an old topic without contributing anything significant to it, it's excusable when you bring something to the topic that hasn't already been discussed, and can be discussed quite well. So basically you can bump the old topic as long as you're contributing enough to it for the bump to be justified.